The disclosed subject matter relates generally to semiconductor devices and, more particularly, to modeling memory cell skew sensitivity.
Modeling systems are widely used to simulate the performance of integrated circuits, such as metal-oxide-semiconductor field-effect transistors (MOSFETs) and combinations thereof. Device modeling allows designers to simulate the feasibility of circuit designs.
A commonly modeled integrated circuit device is a memory cell, such as a static random access memory (SRAM) cell. A typical SRAM cell includes three transistor pairs, a pass transistor pair, a pull-down transistor pair, and a pull-up transistor pair. Typically, transistors in the cell are fabricated to be substantially the same, but due to process variation, there is a mismatch for the threshold voltages of the transistors. The cell and/or transistor mismatches affect the stability of the memory cell.
SRAM modeling involves the use of statistical models that address the likely process variation and attempt to identify the operating parameters of the SRAM cell over the expected range of values. When evaluating an SRAM cell design, it is useful to simulate operation of the cell to determine read and write stability. Common stability parameters are access disturb margin (ADM) for read stability and write margin (WRM) for write stability. The margin of the cell is generally defined as a ratio between the critical current to maintain SRAM stability (ICRIT) to the sigma of ICRIT.
Typical modeling techniques for modeling cell margin assume a constant ICRIT sensitivity to transistor mismatch (i.e., threshold voltage skew between the paired transistors). However, because ICRIT sensitivity does vary with threshold voltage skew, this simplifying assumption introduces error into the simulation, thereby affecting design and hardware correlation.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the disclosed subject matter described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the disclosed subject matter. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art. The disclosed subject matter is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.